Add python virtual env instructions

This change adds instructions on how to setup a python virtual env for this
repo.
In addition, the respective requirements files have been added for easy
installation with pip.

.gitignore

@@ -1 +1,4 @@
+generated_python/__pycache__/
 qr/
+venv/
+

README.md

@@ -28,6 +28,18 @@ For printing QR codes, the qrcode module is required
 
     pip install qrcode[pil]
 
+### Alternative installation method
+
+Alternatively, you can use a python virtual env for the dependencies:
+
+    python -m venv venv
+    . venv/bin/activate
+    pip install -r requirements-buildenv.txt
+    pip install -r requirements.txt
+
+The requirements\*.txt files contain all the dependencies (also the optional ones).
+To leave the python virtual env just call `deactivate`.
+
 ## Technical background
 
 The export QR code of "Google Authenticator" contains the URL `otpauth-migration://offline?data=...`.

extract_otp_secret_keys.py

@@ -78,7 +78,7 @@ def save_qr(data, name):
 def print_qr(data):
     qr = QRCode()
     qr.add_data(data)
-    qr.print_tty()
+    qr.print_ascii()
 
 i = j = 0
 for line in (line.strip() for line in fileinput.input(args.infile)):

requirements-buildenv.txt

@@ -0,0 +1 @@
+wheel

requirements.txt

@@ -0,0 +1,3 @@
+protobuf
+qrcode
+Pillow